Overt diabetic nephropathy (DN) is very slow to develop, but once initiated progresses rapidly. We postulate that early in the course of diabetes, NO availability is increased in part due to the recruitment of the vascular NO2 as a NO source. NO likely protects against the adverse cellular effects of hyperglycemia and by dilating the efferent arteriole (EA) prevents glomerular hypertension (HTN). Thus, HTN mechanisms do not play a significant role during this slow initiation phase. However, with endothelial dysfunction and NO loss over time the EA constricts and there is a further upregulation of endothelium derived hyperpolarizing factor(s) (EDHF), which unlike NO, can only dilate the AA, but not the EA. This increase in EA>AA resistance results in glomerular HTN. EDHF also impairs myogenic autoregulation with further exacerbation of glomerular HTN and overt DN develops. Consistent with the hypothesis, preliminary data show that the Sprague-Dawley (SD) rats from the two major suppliers, Harlan (H) and Charles River (CR) differ greatly in NO availability (CR NO; H NO) and in their susceptibility to DN. Specific Aim 1 will test the hypothesis that the NO availability profile will evolve differentially during the temporal course of streptozotocin (STZ) diabetes in (H) and (CR) rats and changes in NO availability will be paralleled by postulated changes in renal endothelial hemodynamic function (NO, EDHF and prostaglandin dependent dilation), BP transmission parameters and DN susceptibility. Additionally, the hypothesis will be tested that the BP response to L-NAME at 10-14 days after diabetes will predict the subsequent severity of DN in individual rats at 4-6 months. Specific Aim 2 will test if interventions that increase NO availability in (H) rats (dietary nitrite and/or arginine supplementation, tempol, tetrahydrobiopterin) or reduce it in (CR) rats (nitrite free diet + L-NAME) have the predicted effects on DN. Additionally, parallels and differences between diabetic (H) rats and the diabetic eNOS-/-, which do develop advanced DN pathology will be assessed. Specific Aim 3 will use the in-vitro perfused hydronephrotic kidney model to test the hypothesis that DN is associated with EDHF > NO in the renal microcirculation resulting in a relative EA>AA vasoconstriction and increased PGC. Relevance these investigations should provide new insights into the roles of nitric oxide availability, endothelial dysfunction and increasing glomerular pressures as determinants of the course and susceptibility to DN.